Focus-dose co-optimization based on overlapping process window

1. A method of improving a lithographic process of imaging a portion of a design layout onto a substrate using a lithographic apparatus, the method comprising:

during or before the imaging, adjusting, by a hardware computer system, a first processing parameter among processing parameters of the lithographic process to cause the imaging to be more tolerant to perturbations of at least one of the processing parameters; and

during or before the imaging, adjusting, by the hardware computer system, a second processing parameter among processing parameters of the lithographic process to cause the imaging to be more tolerant to perturbations of at least one of the processing parameters,

wherein adjustment of the first processing parameter and/or of the second processing parameter is under a constraint on an amount of adjustment such that the adjusting of the first and second processing parameters cannot adjust the first and second processing parameters, at a particular time, to both their values that cause the imaging to be maximally tolerant to perturbations of the first and second processing parameters.

2. The method of claim 1 , wherein the first processing parameter is dose, and/or wherein the second processing parameter is focus.

3. The method of claim 1 , wherein the first and second processing parameters are adjusted alternately, or wherein the first and second processing parameters are adjusted simultaneously.

4. The method of claim 1 , wherein causing the imaging to be more tolerant to perturbations of at least one of the processing parameters comprises (1) causing values of the processing parameters to be closer to an overlapping process window (OPW) of the portion if the values of the processing parameters are outside the OPW, or (2) causing values of the processing parameters to be farther away from a boundary of the OPW if the values of the processing parameters are inside the OPW.

5. The method of claim 4 , wherein the OPW is a fitted OPW.

6. The method of claim 1 , wherein the first processing parameter is focus and wherein adjusting the first processing parameter comprises moving or tilting the substrate.

7. The method of claim 1 , wherein adjusting the first processing parameter or the second processing parameter comprises calculating a cost function that is a function of the processing parameters and that measures distances of a point in a space of the processing parameters to the boundary of an overlapping process window (OPW) of the portion.

8. The method of claim 7 , wherein adjusting the first processing parameter or the second processing parameter further comprises obtaining values of the processing parameters that minimize or maximize the cost function.

9. The method of claim 1 , further comprising optimizing the lithographic apparatus, and/or further comprising optimizing the portion of the design layout.

10. The method of claim 1 , further comprising obtaining an overlapping process window (OPW) of the portion or of an entirety of the design layout.

11. The method of claim 1 , further comprising obtaining a nominal condition, and/or further comprising determining deviations from a nominal condition.

12. The method of claim 1 , further comprising determining the perturbations.

13. The method of claim 1 , wherein adjusting the first processing parameter causes the imaging to be more tolerant to perturbations of another processing parameter different from the first processing parameter; or wherein adjusting the second processing parameter causes the imaging to be more tolerant to perturbations of another processing parameter different from the second processing parameter.

14. A computer program product comprising a non-transitory computer readable medium having instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to at least:

during or before imaging of a lithographic process of imaging a portion of a design layout onto a substrate using a lithographic apparatus, adjusting a first processing parameter among processing parameters of the lithographic process to cause the imaging to be more tolerant to perturbations of at least one of the processing parameters; and

during or before the imaging, adjust a second processing parameter among processing parameters of the lithographic process to cause the imaging to be more tolerant to perturbations of at least one of the processing parameters,

wherein adjustment of the first processing parameter and/or of the second processing parameter is under a constraint on an amount of adjustment such that the adjustment of the first and second processing parameters cannot adjust the first and second processing parameters, at a particular time, to both their values that cause the imaging to be maximally tolerant to perturbations of the first and second processing parameters.

15. The computer program product of claim 14 , wherein the first processing parameter is dose, and/or wherein the second processing parameter is focus.

16. The computer program product of claim 14 , wherein the first and second processing parameters are adjusted alternately, or wherein the first and second processing parameters are adjusted simultaneously.

17. The computer program product of claim 14 , wherein causing the imaging to be more tolerant to perturbations of at least one of the processing parameters comprises (1) causing values of the processing parameters to be closer to an overlapping process window (OPW) of the portion if the values of the processing parameters are outside the OPW, or (2) causing values of the processing parameters to be farther away from a boundary of the OPW if the values of the processing parameters are inside the OPW.

18. The computer program product of claim 14 , wherein a value of the first processing parameter is subject to one or more limitations.

19. The computer program product of claim 14 , wherein the instructions configured to adjust the first processing parameter or the second processing parameter are further configured to calculate a cost function that is a function of the processing parameters and that measures distances of a point in a space of the processing parameters to the boundary of an overlapping process window (OPW) of the portion.

20. A computer program product comprising a non-transitory computer readable medium having instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to at least:

during or before imaging a portion of a design layout onto a substrate using a lithographic process and a lithographic apparatus wherein the lithographic process has a nominal condition of first processing parameter of the lithographic process and a nominal condition of a second processing parameter of the lithographic process, adjust the first processing parameter to cause the imaging to be more tolerant to perturbations of at least one of a plurality of processing parameters of the lithographic process; and

during or before the imaging, adjust the second processing parameter to cause the imaging to be more tolerant to perturbations of at least one of the processing parameters,

wherein the first processing parameter is being adjusted to a value of the first processing parameter different than the nominal condition of the first processing parameter and/or the second processing parameter is being adjusted to a value of the second processing parameter different than the nominal condition of the second processing parameter.